Someties the Support units 'just' moved into the HQ from a higher HQ, so they can't be sent on to Divisions. The division may be out of range, or that SU may have already been in combat, so it is ready to move into the new unit. I have completely given up on German SU management, set everything in the game to level 3, and forget about it. I have tried to get Karl, Theodore or whatever and the Sturm Pioneers and (etc.) into the Leningrad Assault Force or the Sevastopol Assault force etc. and failed every time. Having said that, some Axis Aces have seemingly mastered this so don't give up if that is how you want to play. Some Axis players start to sort SU related things out in the 41 mud, when they have a lot of APs and nothing to do operationally. Probably not much help, but I here ya.